Bench Talk

There is no shortage of stories about bizarre Department of Defense programs, but this one is surely in the top tier. Extremely Low Frequency (ELF) signal propagation (we’re talking 3 to 30Hz) allows signals to pass through the earth and throughout the oceans to depths of several hundred feet, allowing a system at a single location to communicate nearly anywhere on the planet. This made it rather appealing for communicating with submerged submarines and might be able to function in the event of a nuclear strike. The idea was championed not just by the U.S., but by the Soviet Union and India as well. Signals degrade rapidly in the ocean, so when a submarine is submerged, it is less likely to receive communication. The purpose of Elf was to reach deeply submerged subs sufficiently to let them know to surface to receive communications through normal (and better) radio communications.

Embedded systems have been almost entirely digital throughout their long history, while RF and microwave technologies were separate subsystems with no effective interface between the two. For many reasons, this “RF/digital divide” should finally be connected.

With the exception of changes to the exterior design, to match the flavor of the decade’s décor and the addition of digital readouts, the microwave oven has pretty much remained the same since its inception. That is, until now, with the advent of new high-power LDMOS RF transistor technology, that outdated kitchen appliance we’ve all come to depend on for heating up our lunches might just be getting a new lease on life.

Bounce radio signals off the moon? Unthinkable! Well it certainly was in 1945, when scientists at the U. S. Army Signal Corps at Fort Monmouth (Wall Twp., NJ) resuming trying (after World War II ended) to pierce the Earth's ionosphere with electromagnetic energy. Hardly anyone knew much about this program called “Project Diana” (named for the Greek goddess of the moon), and many still don’t today. This is a shame, as the project and its key participant removed one of the greatest obstacles to space travel.

USB-powered spectrum analyzers aren’t new and some are truly tiny -- just a bit bigger than a flash drive. Some have surprisingly good performance over very wide frequency ranges. The least expensive of these “instruments in a stick” is less than $100. However, every once in a while one comes along that reshuffles the deck, and the latest is the RSA306 from Tektronix. While I rarely extol the virtues of any signal product in these blogs, this one has some features that make it very interesting and suited for applications that are way beyond what instruments like this are typically used for.

When it comes to strange applications, the “ether” arguably has more than its share. To prove it, in my next few blogs I’m going to look at a few that have caught my attention over the years, and one that definitely meets the criteria for “Weird RF” is the Frequency Active Auroral Research Program (HAARP), a program administered by the Office of Naval Research and funded by U.S. Air Force and Navy, and DARPA, and located in Gakona, AK (2010 census: population 218). Work began in 1990 and it was made fully operational and instrumented in June 2007. The prime contractor was BAE Systems Advanced Technologies.

Welcome to the world of microwave systems, or at least those destined for service in defense systems. Owing to the unique requirements of radar, electronic warfare, and other applications, as well as politics, and a “stovepipe” mentality, the U.S. Department of Defense (DoD) is the owner of a broad array of systems designed for a single platform and incompatible with others. It’s a bit like building “one-off” washing machines for each customer.

If you’re a ham and haven’t been active for a while, I have the just the ticket: Get involved with someone who just got the bug (no pun intended), and is ecstatic about making his or her first contacts. I speak from experience here.

On Oct. 31, 2013, Broadcast Engineering, a publication I’ve been reading for 20 years, closed its doors. The company chose to throw in the towel rather than retreating to “digital only”, typically the last gasp before the grave. I learned this not from the company itself but from my colleague Lynnette Reese who sent me a link to back issues (of which there are 340) on a site her Ham dad found: americanradiohistory.com. She blogged about it too, but I had to take a description of this site a step further, as it is absolutely every bit the “gem” she described. It’s also hardly a secret as Alexa ranks it 147,429 in the U.S., placing it above most trade journal sites, but it was a revelation to me.

When in 1945 Raytheon’s engineer Percy Spencer accidently discovered the potential of RF energy for heating food (or in Spencer’s case, for melting a chocolate bar in his pocket), the device generating that energy was a magnetron. Sixty years later, this venerable “vacuum electron device” is still powering everyone’s microwave ovens, making it the only consumer product still using a vacuum tube rather than a semiconductor for any purpose. However, this last bastion of vacuum tubes in consumer electronics may soon be relegated to history now that RF power transistors have achieved the required RF output power, efficiency, and ruggedness required to replace them.